Question

A 30 km journey has to be completed at an average speed of 60 km/hr. If the first 14km is covered at 84 km/hr what must be the average speed for the remainder of the journey​

Answer 1

Answer:

The total distance which train have to cover is 80 km.

Now train covers 60 km at the speed of 40km/h.

So here distance (d1) is =60km

And speed (s1) is = 40km/h

Time taken to cover this distance (t1)= d/s= 60/40= 3/2 hrs.

Further train covers 20km (remaining distance) at the speed of 20km/h.

Here distance(d2)=20km

And speed (s2)=20km/h.

Time (t2)=d2/s2= 20/20= 1 hrs.

Total distance =d1+d2= 60+20= 80 km

Total time =t1+t2= 3/2+1= 5/2 hrs.

Average speed = total distance /total time

Average speed =80 ÷5/2= 80×2/5= 16×2= 32 km/h

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Answer 2

The total distance which train have to cover is 80 km.

Now train covers 60 km at the speed of 40km/h.

So here distance (d1) is =60km

And speed (s1) is = 40km/h

Time taken to cover this distance (t1)= d/s= 60/40= 3/2 hrs.

Further train covers 20km (remaining distance) at the speed of 20km/h.

Here distance(d2)=20km

And speed (s2)=20km/h.

Time (t2)=d2/s2= 20/20= 1 hrs.

Total distance =d1+d2= 60+20= 80 km

Total time =t1+t2= 3/2+1= 5/2 hrs.

Average speed = total distance /total time

Average speed =80 ÷5/2= 80×2/5= 16×2= 32 km/h

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